1. Field of the Invention
The present invention relates to a downhole tool. In particular, but not exclusively, the present invention relates to a tool for generating a force downhole and to a method of generating a force downhole.
2. Description of the Related Art
As is well known in the oil and gas exploration and production industry, access to subterranean hydrocarbon bearing formations is achieved by drilling a borehole to a desired depth and casing\lining the borehole with tubing. Strings of smaller diameter tubing and downhole tools are often located within the casing\liner for performing desired downhole functions. These tubing strings and tools may require to be fixed relative to the casing\liner, and this is typically achieved using dedicated downhole locks, which may include locking dogs that are radially movable to engage a recess in a wall of the casing\liner.
Downhole tools or tubing strings including such locks are typically run into the casing\liner with the locking dogs in a retracted position, to allow passage of the string through the tubing. Once the string has been located in the desired position, the lock is activated to engage the locking dogs in the recess. Examples of existing locks include the Otis Engineering lock, commercially available under the X-LINE trade mark, and the Baker Oil Tools lock, commercially available under the SUR-SET trade mark. These locks are of a “jar up to release” type, where a force is exerted on the lock, via a fishing neck, in an upward direction (along the borehole towards the surface) to release the lock.
Locks of this type suffer from the disadvantage that the direction of release of the lock is the same as the direction of flow of well fluids through the borehole. Accordingly, it has been found that there is a tendency for the fishing neck to vibrate and creep upwardly, especially in a severe or heavy flow situation, which can cause premature release.
Alternative locks are of a “jar down to release” type where a force is exerted in a downward direction to release the lock. In locks of this type, flow of well fluids does not cause premature release and in fact tends to further energise the lock, and these locks are often selected for this reason. One such lock is commercially available from the applicant under the UNISET QX trade mark.
However, it is generally preferred to exert an upward jarring force to release a lock in the downhole environment, for reasons including that it is safer to exert a large force by jarring up compared to jarring down and, furthermore, an upward jarring can be performed using wireline\slickline. As is known in the art, wireline\slickline offers advantages in terms of speed of tool\tubing deployment and recovery.
It is among the objects of embodiments of the present invention to obviate or mitigate at least one of the foregoing disadvantages.